The present invention relates to the preparation of non-whiteware ceramic articles.
Ceramic articles are generally manufactured by processes involving pressing, casting or plastic-forming. Examples of pressing include uniaxial pressing, isostatic pressing, dry pressing, hot uniaxial pressing, hot isostatic pressing and hot dry pressing. Examples of casing include slip casting, drain casting, tape casting, thixotropic casting, pressure casting and soluble casting. Examples of plastic-forming methods include extrusion, injection molding, transfer molding and compression molding.
One example of a manufacturing method, slip casting, is a well-known and ancient process by which ceramic articles are prepared. In this method, the particulate matter is suspended in a slip medium, often water, to form a slip. The slip is poured into a mold and a portion of the slip medium is drawn out of the casting slip through the mold leaving a cast behind in the mold. The mold and cast are then separated and the cast article is processed to give it the final properties desired. Slip casting is employed in the manufacture of a wide variety of products, both whiteware and non-whiteware, ranging from sanitary ware to laboratory ware to electronic ceramics.
Dry pressing is also a well-known practice by which ceramic articles are prepared. In dry pressing, a particulate material is suspended in a slip medium, generally with other additives selected to control both the properties of the slip and the article ultimately prepared from the slip. The solvent is removed to prepare a powder having particles of the desired size or range of sizes. This powder is then placed into dies having the desired shape and pressure is applied to form the green ceramic article which undergoes additional processing. The pressure involved in dry pressing is applied either unilaterally as in dry pressing or from all directions as in isostatic dry pressing. Pressing operations may be carried out at various temperatures including room temperature or elevated temperatures.
Extrusion is another well-known process for the formation of ceramic articles. In a typical extrusion process, a ceramic powder is moistened and then kneaded or pugged until it forms a plastic mass which is extruded through a die to form the green ceramic article which then undergoes additional processing.
A major problem experienced in the preparation of non-whiteware ceramic articles by any of the methods known in the art as identified or described above is low green strength. Low green strength of articles is detrimental due to the breakage of articles during processing.
What is needed is an additive, useful in casting, pressing and plastic-forming processes for the manufacture of non-whiteware ceramic articles that results in increased green strength of the articles produced and that does not adversely impact other properties of the articles or the slip from which they are prepared.